The present invention relates to preventing the direct exposure of relatively cool suction gas in a reciprocating compressor to compressor components heated by discharge gas.
The volumetric efficiency of a refrigeration compressor is directly affected by the temperature of the suction gas undergoing compression therein. Volumetric efficiency is the ratio of the actual weight of refrigerant compressed in a compressor cylinder, in operation, to the weight of the refrigerant the cylinder can theoretically hold. Suction gas is the relatively cool refrigerant vapor which is returned from the evaporator in a refrigeration system to the compressor. The actual volume and therefore the weight of the refrigerant vapor which flows into a compressor cylinder from an evaporator is always less than the theoretical volume of refrigerant which would flow into the cylinder if it were communicated to the cylinder at exactly the same temperature and pressure it left the evaporator.
Among the reasons the weight of the suction gas compressed in a compressor cylinder is less than the theoretical maximum is the fact that the walls of the compressor cylinder and other compressor components to which suction gas is exposed in its travel from the evaporator to the cylinder are considerably hotter than the refrigerant vapor received from the evaporator. As a result of its travel from the evaporator and past such heated components in the compressor suction gas flow path, suction gas temperature is increased prior to the start of the compression process. It follows then that the actual weight of the refrigerant delivered into the cylinder of a reciprocating compressor is less than the theoretical maximum weight due to the expanded volume of the refrigerant found in the cylinder prior to compression. The volumetric efficiency of the compressor suffers as a result.
The effect of such suction gas heating is particularly notable in the increasingly compact hermetic compressors currently being produced. In such compressors, wall thicknesses have been decreased and single walls are often used to define and separate two disticnt refrigerant flow paths within a compressor. Exemplary in this regard is the cylinder head illustrated in FIG. 2 of U.S. Pat. No. 3,817,661. Other illustrative patents are U.S. Pats. Nos. 3,926,009 and 3,971,407 in which suction gas is directly exposed to the compressor cylinder head assembly and U.S. Pats. Nos. 4,100,934; 4,382,749 and 4,411,600 in which the suction gas inlet passage is integral within the cylinder head/valve plate assembly.
Further, when suction gas is superheated the compression process is also affected from the standpoint of compressor energy consumption. This effect is a negative one and is one which causes the energy efficiency ration (EER) of the system in which the compressor is located to suffer. By reducing suction gas superheating the compression process becomes a more efficient one.
The problem of suction gas heating within a compressor is specifically addressed in U.S. Pats. Nos. 4,371,319; 4,411,600 and 4,549,857. U.S. Pat. No. 4,371,319 teaches an elaborate heat insulating arrangement in which compressor discharge components including the head cover, discharge silencer and discharge tube are coated by a heat insulating material. U.S. Pat. No. 4,411,600 teaches a plastic suction pipe by which suction gas is guided to a suction chamber. As earlier mentioned however, this patent nonetheless teaches the exposure of suction gas to high temperature compressor components in the immediate vicinity of the cylinder head assembly. Finally, U.S. Pat. No. 4,549,857 teaches a plastic suction inlet ad seal component in a compressor which is used in conjunction with a gasket for sound attenuation and suction gas insulating purposes. Suction gas is communicated into an internally molded suction chamber through dual inlet tubes in the inlet/seal component. The inlet/seal component and suction chamber surround the inlet openings of the valve plate assembly. The inlet/seal component is separated from the cylinder head by the aforementioned gasket.
As should be apparent from the number of recently-issued related patents, any manner in which suction gas heating can be minimized and the volumetric and/or energy efficiency of a refrigerant compressor increased, particularly at minimal expense and without unduly complicating the manufacture of the compressor, represents a significant advance in the compressor art.